This invention relates to a method of processing thermoplastics or thermosetting plastics using batchwise operating device. The device includes a cylindrical container with a shaft disposed coaxially therein, the shaft being provided with mixing tools and drivable at high speed. The material to be processed, and if required liquid, is supplied to the container in predetermined amounts, gelled by the resultant frictional heat, granulated if necessary, then expelled from the container. The present invention also relates to an apparatus for carrying out the method.
In a method of this kind, known from German Auslegeschrift 11 18 959, the plastic raw materials are supplied batchwise to the device described hereinabove, together with colorant, filler, stabilizers, internal lubricants and the like, then gelled by the internal frictional heat generated during operation of the shaft provided with mixing tools, and granulated if necessary. The process and the device described hereinabove have proven extraordinarily satisfactory in practice, since the processing time is only approximately 30-180 seconds.
An improvement on the device described hereinabove is known from U.S. Pat. No. 3,266,738, wherein a shearing screw is disposed on the shaft outside the container, but connected with the latter via an opening, the shearing screw serving to chop plastic scrap and feed it to the container in order to allow processing of such plastic scrap. In this known device, the mixing tools are designed to serve simultaneously as cutting tools.
U.S. Pat. No. 3,163,403 discloses a continuously operating device for processing thermoplastics and thermosetting plastics in a single work step; this device includes a cylindrical mixing container with a shaft provided with mixing tools, the shaft being disposed coaxially therein and drivable at high speed. A material inlet is provided at one end of the container and a material outlet is provided at the other end of the container. Injection nozzles for a liquid to be supplied are provided along the container and/or along the shaft. A mixing and heating zone followed by a cooling zone are provided next to the material inlet opening. The shaft is provided with mixing arms of different numbers and designs in the mixing and heating zone and the continuous cooling zone. Alternatively, the shaft can be driven in the cooling zone at a lower speed than in the mixing and heating zone. This is intended to ensure that a great deal of energy is conducted into the material in the mixing and heating zone by the mixing tools, while in the contiguous cooling zone only a small amount of energy is added, since this area is designed for the removal of heat. This continuously operating device necessarily presupposes a certain machine size and a certain material throughput in order to operate satisfactorily, i.e., a continuously operating machine of this type can only operate economically in large installations.
In terms of the uniformity of processing of the material, batchwise operating devices are always optimal, because in this case there is a higher probability that all of the material particles will be charged with energy to the same degree. This is especially true of smaller machines and smaller throughput volumes.
However, a general disadvantage of devices which operate batchwise is that the complete cycles are relatively long, because a great deal of time is lost in metering the charge and loading the device with the charge, starting the device, and stopping and emptying the device. In addition, the charging time periods, i.e., the time periods required for filling, starting, and stopping and/or emptying, i.e., the time periods spend in handling alone, are relatively long.